This invention relates to a dry photographic printing process, based on the use of photochromic materials, which permits to obtain high quality photographs by means of conventional electronic equipment. The invention is also applicable to the reproduction of color prints.
Photochromic materials, viz. materials which are colorless, but develop colors when irradiated with light of specific wavelength, have been known in the art for a long time. Each photochromic material is sensitive only to a given light wavelength and will not acquire color if it is irradiated with light of a different wavelength.
The light sensitivity of photochromic materials has led to new types of self-developing and dry photography, which are known in the literature for more than 20 years. They are used as color-forming components in photochromic and free radicals, photographic materials with a sensitivity of 10-4 j.cmxe2x88x922(see Photochronism, R. C. Bertelson, Willy Interscience New York, Ed C. H. Brown (1971) and A. L. Kartuzhaqnsi (Ed), Non-silver photographic processes, Izd. Khimiya, Leningrad 1984).
The photochromic materials are also used in the technology of photomasking and photoresist (see P. L. Foris (N.C.R.), U.S. Pat. No. 3,346,385, 1967, and M. Orlovoic, E. Stone and J. M. Pearson, J. Electrochem. Soc., 116 (1969), p. 1464).
Many applications in the field of imaging and reprography systems have been suggested using metal salts and different supports or reactants.
A record sheet for thermographic copying or hot stylus recording has a coating consisting of an intimate Ore of solid calcium resinate and 4xe2x80x2,7xe2x80x2,8xe2x80x2-trimethoxy-BIPS. These react upon melting to give a stable, deep blue color, and various colors can be obtained from other combinations of cations and spiropyrans (see H. H. Baum, U.S. Pat. No. 3,293,055, 1966; L.D. Taylor, Polaroid, U.S. Pat. No. 3,320,067,xe2x80x9cComposition and process utilizing photospiransxe2x80x9d, 1967; P. L. Foris, U.S. Pat. No. 3,341,330,xe2x80x9cMethods of forming thermally stable photochromic dyes and productsxe2x80x9d, 1967; W. J. Becker and P. L. Foris, U.S. Pat. No. 3,364,023, 1968).
The influence of a polymer on the characteristics of the photochromic transformation, and the possibility of stabilizig the colored form by selecting the appropriate polymer or the type of chemical binding of the spiropyran to the latter, are discussed by M. Kryszenski, B. Vadovski and R. IuhoLf, Macromol. Chem., 183 (1982), p. 1257; G. Smets, J. Brackem and M. Iril, Pure Appl. Chem., 50 (1978), p. 1979; and M. Le Baccon, F. Garnier and R. Guglielmetti, Bull. Soc. Chim. Fr. (1979), p. 315.
When paper or plastic materials containing a spiropyran are irradiated through a negative transparent original, colorless spiropyrans is transformed, in the region exposed to ultraviolet radiation, into colored photomerocyanine set in this form by the vinylic polymer of binder. This process yields a negative image of the original (see Z. G. Gardlund and J. J. Laverty, J. Polym. Sci., B 7(1969), p. 719; and C. Ceintrey, R. Guglielmetti and M. Le Baccon, French Patent Application No. 76.15336, 1976).
As is well known, different colors may be obtained by additive synthesis or subtractive synthesis, which are both conventionally used, e.g. in color printing. This invention will be described as based on additive synthesis, but subtractive synthesis is not excluded. Further, the colors used for the synthesis could be the basic colorsxe2x80x94magenta, yellow and cyanxe2x80x94or the complementary colorsxe2x80x94respectively green, red and bluexe2x80x94or, in particular cases, other combinations of colors. In describing this invention, it will be assumed that complementary colors (briefly, the RGB system) are used, but this is not to be construed as a limitation. Any method or procedure known in the art for the production of desired colors by additive or substractive synthesis can be used in carrying this invention into practice.
Despite the extensive knowledge of photochromic materials which is available in the art, no satisfactory photographic process based on their use has been developed so far.
It is the purpose of this invention to provide such a process for dry printing and photography.
It is an another purpose to provide such a process that produces stable prints.
It is a further purpose to provide such a process that produces high quality photographs.
It is a still further purpose to provide such a process that can be carried out by using conventional electronic equipment.
It is a still further purpose to provide such a process that can be used for the reproduction of printed color images.
It is a still further purpose to provide personalized printing, in which changes in a part or all of the output can be effected as a function of a predetermined rule, to prevent counterfeiting.
The process of color photography or reproduction of color prints according to the invention comprises the steps of:
axe2x80x94providing a substrate having at least three and preferably four superimposed layers, including photochromic materials sensitive to light wavelengths different from layer to layer;
bxe2x80x94scanning the object to be photographed or reproduced;
cxe2x80x94generating from the scanning a digital file defining the image of the object, to be created on the photograph or reproduced;
dxe2x80x94providing at least three and preferably four sources of laser light having different wavelengths, each of which is the wavelength to which one of said photochromic materials is sensitive, while the other photochromic materials are not sensitive to it; and
exe2x80x94irradiating the substrate by means of the laser beams produced by said sources, according to a program determined by said digital file, whereby to develop in each pixel of the substrate the color that it has in said image.
Any substrate layer that is not irradiated or is irradiated with a light wavelength to which the color of the layer is not is sensitive, is unaffected and if or where transparent, it remains transparent. In the following description, it will be assumed that the RGB system is used and therefore the aforesaid substrate layers include photochromic materials which, when irradiated by the appropriate light wavelength, will produce in each layer one of the aforesaid complementary colors: red, green and blue, and optionally, in one layer, black. However, this is not intended to be a limitation, and, for example, the basic colors magenta, yellow and cyan might be produced.
The digital file, defining the image, may be obtained by scanning the object to be photographed, viz. by scanning in vivo. Thus, e.g., a digital file representing the face of a person can be obtained by scanning said face. This technique and the scanner apparatus for carrying it out are well known. The results of the scanning is a file which determines the color of each pixel of the photograph. If the invention is used for reproducing a color print, the color print will be scanned.
Once the digital file has been created, the laser beam sources are controlled by it, to develop the appropriate color in each pixel of the substrate by generating and directing onto said pixel the laser beam the wavelength of which sensitizes the photochromic material which, when sensitized, assumes said appropriate color. Though black is not properly a color, what is said herein about the colors applies to it as well. In other words, the digital file will control the laser sources in such a way that if a given color is desired to be developed at a given pixel, it will activate the laser beam that develops said color when impinging on one of the layers of the substrate including a photochromic material (hereinafter, briefly, xe2x80x9ca photochromic layerxe2x80x9d). If the photochromic layer which develops said color is not the top one, the laser beam will cross the superimposed layers without affecting them in any way, because the photochromic materials of said superimposed layers are not sensitive to the wavelength of said beam and therefore said layers will be and remain transparent. It will be understood that, when reference is made to a pixel of the substrate, the pixel is defined in the layer that is developed. In correspondence to said pixel, the superimposed layers are unaffected by the radiation.
The additive synthesis is due to the fact that if the pixels are sufficiently small, the human eye combines the colors of adjacent pixels. The subtractive synthesis requires a white background, from which one or more basic or complementary colors are filtered out, as well known in the art.
If a less than perfect image is considered satisfactory, less than three complementary colors can be used, in a way that is well known to persons skilled in the color printing. In particular cases, different combinations of colors can be used in the photochromic layers of the substrate, or a different background layer can be provided, in ways that will be apparent to persons skilled in the art. Also, an uppermost transparent and colorless layer can be added to protect the image.
The size of the pixels is a relevant parameter and is decided according to the particular use of the invention and for the particular degree of resolution desired. For instance, if it is desired to produce a large image that will be seen only from a distance, the pixels can be much larger than for an ordinary photograph.
If it should be desired to carry out the invention using a subtractive synthesis, a white background will be provided in the bottom layer of the substrate and the various photochromic layers will be so irradiated as to subtract from the white the colors complementary to the color that should be developed in each particular pixel.
In a preferred form of the invention, the printing process further comprises setting the color developed by irradiation in each pixel of the substrate layers; and setting the background of each of said substrate layersxe2x80x94viz. the areas developed of the substrate layers in which no color has been developed by irradiation. By the expression xe2x80x9csetting the backgroundxe2x80x9d is meant herein rendering the color or lack of color or transparency of said non-irradiated areas, viz. of all the pixels thereof, so that a color or a different color may not be developed therein, or more precisely in the photochromic materials included therein, by accidental irradiation or irradiation applied for another purpose. Hereinafter, the expression xe2x80x9csetting the colorxe2x80x9d of a pixel or area should be construed as meaning rendering its chromatic condition permanent, whether said chromatic condition should consist in the presence or in the absence of a color or in a state of lack of color and transparence.
Means for setting a photochromic material and rendering its color or absence of color stable and affected by irradiation of any wavelength, are known in the art. One means is the application of heat. The application of heat may be associated with an irradiation. Other means consist in modifications of the molecule of said material by chemical means, and are described e.g. in M. Kryszenski et al., Macromol. Chem. 183 (19820 1257); G. Smets et al., Pure Appl. Chem., 50 (1978) 1979; M. Le Baccon et al., Bull. Soc. Chim. France, 8 (1979) 315, A. Hinnen et al., Bull. Soc. Chim. France 8 (1968) 2066, and R. Guglielmetti et al., Bull. Soc. Chim. France 8 (1967) 1967 2824.
Therefore, the preferred form of the photographic printing of this invention, comprises the steps of:
axe2x80x94providing a substrate having at least three and preferably four superimposed layers, including photochromic materials sensitive to light wavelengths different from layer to layer;
bxe2x80x94scanning the object to be photographed or reproduced;
cxe2x80x94generating from the scanning a digital file defining the image of said object, to be created on the photograph or reproduced;
dxe2x80x94providing at least three and preferably four sources of laser light having different wavelengths, each of which is the wavelength to which one of said photochromic materials is sensitive, while the other photochromic materials are not sensitive to it;
exe2x80x94irradiating the substrate by means of the laser beams produced by said sources, according to a program determined by said digital file, whereby to develop in each pixel of the substrate the color that it has in said image;
fxe2x80x94setting the colors thus generated in the pixels of the substrate layers; and
gxe2x80x94setting the background areas of the substrate layers.
The various steps set forth hereinbefore need not be separate ones carried in the order in which they have been listed. For example, an irradiation and a setting step may be carried out concurrently.
The settings may be carried out in various cases by heating alone or by irradiation alone or by a combination of heating and irradiation of said substrate layers.